A number of wastewater treatment systems having a variety of features and using a variety of treatment methods are known in the art including U.S. Pat. Nos. 3,251,471, 3,327,855, 3,476,682, 3,679,053, 3,721,344 and 3,834,536. Many prior art single home or small community wastewater treatment systems are anaerobic units such as septic tanks. Other prior art single home or small community wastewater treatment systems are aerobic units.
One disadvantage of systems using aerobic treatment methods is that effluent therefrom will likely contain substantial amounts of nitrate which can cause algae blooms in receiving water. High concentrations of nitrate in drinking water can also cause methemoglobinemia in infants. Controlling Wastewater Treatment Processes, Dan Cortinovis, Ridgeline Press, 1984, p. 15.
One disadvantage of systems using anaerobic treatment methods is that effluent therefrom will likely contain substantial amounts of ammonia created from the decay of proteins and urea in raw sewage. Ammonia in the un-ionized form is toxic to fish and other aquatic life, especially when the receiving water is of a relatively high pH. Further, the ammonia creates an oxygen demand in the receiving water and then, as in aerobic treatment methods, nitrate is produced. In turn, the nitrate may cause algae blooms which increase the pH of the receiving water, making additional ammonia even more toxic. Controlling, pp. 13-14. By using a combination of aerobic and anaerobic methods, however, ammonia in the wastewater can be converted to relatively harmless nitrogen. Controlling, p. 15.